Dc building system with energy storage and control system

ABSTRACT

A DC building electrical system includes a DC power consuming device connected to a DC bus. A source of DC power is connected to the DC bus and powers the DC power consuming device. An energy storage device is connected to the DC bus and to a DC emergency load. The energy storage device powers the DC power consuming device in conjunction with the source of DC power, and powers the DC emergency load when source of power other than the energy storage device is available to the DC power consuming device.

CROSS REFERENCES TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/684,083 filed on Aug. 16, 2012, entitled “DC MICROGRID BUILDINGENERGY MANAGEMENT PLATFORM” (Attorney Docket No. 13050-40005-US-1), andto U.S. Provisional Patent Application No. 61/699,169 filed on Sep. 10,2012, entitled “DC MICROGRID BUILDING ENERGY MANAGEMENT PLATFORM”(Attorney Docket No. 13050-40005-US-2). The complete subject matters ofthese patent applications are hereby incorporated herein by reference,in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to advanced component technologies whichmay improve building energy efficiency.

2. Description of the Related Art

Current AC building systems do not use locally-generated renewableenergy in the most cost effective way and require a very reliableutility grid connection, resulting in excess life-cycle costs as well asenergy security concerns. It is known to utilize batteries as an energybuffer for a PV array, but such systems do not eliminate wasteful ACconversions when addressing the most common building electrical loads,such as lighting and ventilation. Likewise, it is known to provide asmart building energy management system, but such systems do notincorporate a DC microgrid to improve efficiency and energy security.FIG. 1 is a block diagram of one embodiment of a conventional ACreference system for comparison with the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to a DC microgrid without an inverter.The DC microgrid powers one or more DC powered devices, which caninclude lighting and cooling devices. The DC microgrid offers moreefficient use of DC power generated by a Photovoltaic (PV) array. The DCmicrogrid is less expensive to implement than conventional PV systemsand offers improved payback. The DC microgrid enables use of lessexpensive DC powered devices. In various embodiments, the DC microgridcan employ the solar synchronized load and/or maximum power pointtracking control features described in U.S. patent application Ser. No.13/560,726 and U.S. patent application Ser. No. 13/749,604.

In other embodiments, the PV array of the DC microgrid can be sized toprovide an advantageous DC bus voltage range for more efficient MaximumPower Point Tracking (MPPT) control that is lower and/or narrower thanconventional DC bus voltage ranges. Alternatively or additionally, thePV array can be sized to provide power within a predetermined range foradvantageously balancing power production by the PV array and a utilitygrid. For example the PV array can be sized to provide less than halfthe power demand, for example between 25-40% of the power demand.

The Direct Current (DC) Microgrid Building Energy Management Platform(DCMG-BEMP) of the invention offers significant benefits relative toconventional alternating current (AC) building systems in terms ofreduced total cost of ownership (TCO) and increased energy security.Conventional building-level power distribution systems suffer fromAC-to-DC conversion losses in powering many common devices, as well asDC-to-AC losses when utilizing locally produced DC power, such as fromrenewable energy sources. For example, these conversions result in up toa 12% greater loss of energy between photovoltaic (PV) arrays and AClighting loads, when compared to the DC microgrid of the presentinvention. Typical PV systems also require all power to flow throughunreliable and expensive grid-connected inverter hardware, whichprevents the PV power from being used for mission-critical activitieswhen the grid power is lost (blackout condition). In addition, currentAC building systems have limited or no ability to manage building peakpower demands, which can lead to demand charges and further gridinstability. The DCMG-BEMP applies a novel approach to using mature,reliable DC technology and dynamically optimizing power sources, loads,and energy storage system interaction, minimizing TCO and reliance ongrid-based electricity. Economic modeling using the BLCC tool shows15%-25% improvement in Savings to Investment Ratio (SIR) over 25 yearsfor the DCMG-BEMP compared to equivalent AC systems. The presentinvention DCMG-BEMP provides increased energy efficiency, improvedenergy security, and a lower total cost-of-ownership compared to otherapproaches.

The invention may provide a DC microgrid configuration in which DCelectrical energy is stored in order to power DC loads without beingconverted to AC electrical energy. Such DC energy storage may be in theform of batteries, capacitors, flywheels, etc., although only batteriesare shown in the drawings.

One primary advantage of using energy storage in the DC microgridconfiguration is that the energy (e.g., backup power) may be utilizedmore efficiently by the DC loads when in the form of DC from the energystorage elements. One reason for the higher efficiency is that there areno intermediate conversions from DC storage to AC and back to DC, as istypically done in buildings.

Energy storage elements may be incorporated into the DC power supply,making it effectively similar to an uninterruptable power supply (UPS)configuration. Alternatively, energy storage elements may be connectedindependently to the DC bus. However, at least one exemplary embodimentin the drawing includes a battery incorporated into a DC power supply,which is connected to an AC grid and is separate from a solar grid(e.g., a renewable DC energy power source.

An energy storage device may be directly connected to the DC bus, or mayhave intermediate DC/DC converters to optimize voltages and currents forcharging/discharging. An energy storage device may be charged from thegrid through an AC/DC power supply, may be charged from other DC sourcessuch as solar photovoltaic (PV), or may be charged by both of thesemethods.

A relatively small amount of energy storage capacity in the DC microgridmay be used to meet the ninety minute emergency lighting requirement forU.S. buildings, without the need for dedicated emergency lightingcircuits or distributed battery strategies, as is typical. For example,all the lights may be dimmed, and/or only a subset of the lights may beturned on, via software control, in order to meet the emergency lightingbrightness requirement. Using the DC power supply in the uninterruptablepower supply (UPS) mode may enable the DC emergency lighting to bepowered without adding any additional infrastructure to the building. Inthe prior art, in contrast, emergency lighting may require additionalinfrastructure such as separate AC or DC lighting circuits and batterysystems. The inventive arrangement may provide advantages such as lowercost, higher reliability, and flexibility to change which lights areturned on during emergencies, and which lighting levels are availableduring emergencies. These advantages may be realized exclusively via aninventive software configuration.

Larger amounts of energy storage may be included in the DC microgrid toprovide varying levels of backup energy. For example, enough backupenergy may be stored to keep a building operating throughout the nighton most nights in an emergency mode in the event that there is enoughexcess solar PV energy generated during the day to put into energystorage systems and subsequently be used at night in the DC loads whensolar energy is not available. The amount of storage that is requiredmay depend on the amount of power needed in “emergency mode,” (i.e.,lower lighting or ventilation levels may be acceptable in a blackout),and may depend on the amount of solar energy available in differentgeographic regions. These variables may be used to statisticallycalculate the “energy security” or probability of powering the buildingthroughout the night or other desired time period with the excess solarenergy stored from the daytime. Any amount of stored solar PV energy canreduce the amount of diesel or other fuel needed for other backup powergeneration options.

If the DC microgrid incorporates DC thermal loads (e.g., foodrefrigeration, building HVAC, hot water heating), then the thermalstorage may be combined with the electrical energy storage to determinethe “energy security”. For example, frozen food may stay frozen for somehours even when energy storage is depleted, which may provide enoughprotection until solar energy is again available in the morning.Further, the food may be frozen to a temperature several degrees belowwhat is required for freezing, and thus the frozen food itself mayeffectively store energy.

In order to extend the availability of energy storage to keep a buildinguseable in an emergency situation, the electrical loads in the buildingmay be adjusted to adapt to the availability of stored energy, solarpower, and the duration of the blackout (e.g., the duration of the lossof utility grid power). For example, in the first hour of a blackoutoccurring with full sunshine and full energy storage reserves, thelighting, ventilation, or other emergency loads may be kept at fullpower. However, as the duration of the blackout continues into thesecond hour with less sunshine available, the emergency loads may beoperated at lower power levels in order to conserve stored energy. Forexample, lights may be dimmed, ventilation may be operated at lowerspeed, etc. Additional such adjustments may be made to the operation ofthe loads as the duration of the blackout becomes longer, and dependingon the amount of solar energy available. Through adaptive adjustment ofthe emergency loads, the building is more likely to remain in a usablestate through more blackout scenarios, since short-term blackouts occurmore frequently than long-term blackouts, and since weather conditions(e.g., amount of sun) may be very different during different blackouts.

Energy storage which is primarily designed into the DC microgrid for useas backup may also be used for “demand response” purposes to help theutility company manage peak power demands. For example, the utilitycompany may send an electrical signal or provide an incentive (e.g.,time-of-day utility rates or demand charges) for the DC microgrid to usepower from the energy storage and PV for DC loads rather than from theutility grid for a period of time, thus reducing the electricity demandon the utility grid during a peak period (“DC load-leveling”).

Further to the above, the energy storage may be connected to a DC/ACinverter or bi-directional AC/DC converter which would allow the energystorage to also be used to offset peak demands from AC loads in thebuilding or elsewhere on the AC utility grid (“AC load leveling”). TheDC microgrid may be configured to provide a combination of the above—DCload leveling and AC load leveling.

Energy storage in the DC microgrid may have the unique ability to beperiodically tested by feeding some or all of the power for the DC loadsfrom the DC energy storage for test purposes without affecting buildingfunctionality. For example, the lights may not blink during suchtesting. In other words, some or all power may be directed to flow fromthe DC energy storage to the DC loads during the test period,temporarily reducing or eliminating the power needed from the DC powersupply, PV, or other energy source. During this test period, voltagesand/or currents may be measured to validate the rate of discharge anddetermine the health of the storage system. Similarly, solar PV oranother DC power source may be used to charge energy storage anddetermine health of the energy storage system from the charge rate.

Building energy storage elements in the DC microgrid also may be used asan energy supply for commercial electric vehicles used in and around abuilding or complex. For example, the batteries from electric fork-liftsmay be used as part of the building energy storage while they are beingcharged on or off the vehicle, and the batteries from electric golfcarts may be used as building energy storage, etc. The above concept mayalso be used in a conventional AC connection to the building via asingle or bi-directional AC/DC inverter.

Industrial fans or other DC motor loads may be used in the DC microgridas virtual flywheel storage via use of a bi-directional variablefrequency drive (VFD) on the motor connected to the DC bus. This conceptmay also be known as regenerative braking, or generating power from theslowing down of a motor. An advantage of this arrangement is that someshort-term storage is realized through the use of existing motordevices, potentially saving cost through reduction or elimination ofadditional storage elements in the system.

In one embodiment, the invention comprises a DC building electricalsystem including a DC power consuming device connected to a DC bus. Asource of DC power is connected to the DC bus and powers the DC powerconsuming device. An energy storage device is connected to the DC busand to a DC emergency load. The energy storage device powers the DCpower consuming device in conjunction with the source of DC power, andpowers the DC emergency load when no sources of power, or limitedsources of power, (e.g., solar) other than the energy storage device areavailable to the DC power consuming device.

In another embodiment, the invention comprises a DC building electricalsystem including a DC power consuming device connected to a DC bus. Asource of DC power is connected to the DC bus and powers the DC powerconsuming device. An energy storage device is connected to the DC busand to the motor vehicle. The energy storage powers the DC powerconsuming device in conjunction with the source of DC power, and powersthe motor vehicle.

In another embodiment, the invention comprises a DC building electricalsystem including a DC power consuming device connected to a DC bus. Asource of DC power is connected to the DC bus and powers the DC powerconsuming device. An energy storage device is connected to the DC busand powers the DC power consuming device in conjunction with the sourceof DC power. A DC power control system selectively charges anddischarges the energy storage device based on a current state of chargeof the energy storage device and a predetermined target state of chargeof the energy storage device.

In another embodiment, the invention comprises a microgrid systemarrangement including a photovoltaic array producing a DC voltage on aDC bus. A DC power supply produces DC voltage on the DC bus from ACvoltage received from a utility grid. A DC power consuming device isconnected to the DC bus. A controller controls amounts of DC powerprovided to the DC bus by the photovoltaic array and by the DC powersupply.

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the energy storage device,via a common power network, supplies DC power 1) powering DC buildingloads in combination with at least one other DC power source (e.g., arenewable energy DC power source or an AC grid); and 2) powering DCemergency loads for a predetermined period when no other power isavailable.

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the energy storage device isused to power a mobile device used within the building (e.g., a vehiclesuch as a fork lift or a golf cart).

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the DC building systemincludes a DC power control system that selectively charges anddischarges the energy storage device during non-emergency periods basedon a state of charge (SOC) of the energy storage device and apredetermined emergency SOC.

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the DC building systemincludes a DC power control system that charges the energy storagedevice using excess power available from a renewable energy DC powersource.

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the DC building systemincludes a DC power control system that when a state of charge (SOC) ofan energy storage device drops below a predetermined SOC: selectivelyadjusts a variable DC load so that a total load on a solar device isless than an available power of the solar device; and charges the energystorage device to above the predetermined SOC.

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the DC building systemincludes a DC power control system that when a state of charge (SOC) ofan energy storage device drops below a predetermined SOC: controls adischarge rate of the of the energy storage device by selectivelyreducing or discontinuing operation of one or more variable DC loadsbased on a building ambient condition (e.g., amount of sunlight) and acorresponding predetermined building condition (emergency interiorlighting level).

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the DC building systemincludes a DC power control system that selectively reduces ordiscontinues operation of a variable DC load during emergency operationbased on a duration of the emergency.

In another embodiment, the invention comprises a DC building systememploying an energy storage device, wherein the DC building systemincludes a DC power control system that charges the energy storagedevice by discontinuing power to a motor/generator and operating themotor/generator in a regenerative mode during which kinetic energy isconverted to DC power. The motor/generator may also directly power theDC loads from regenerative power, and provide all or part of the energystorage in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a block diagram of one embodiment of a conventional ACreference system.

FIG. 2 is a block diagram of one embodiment of a core DC microgridsystem architecture of the present invention.

FIG. 3 is a block diagram of one embodiment of an enhanced DC microgridsystem architecture of the present invention.

FIG. 4 is a block diagram of another embodiment of an enhanced DCmicrogrid system architecture of the present invention.

FIG. 5 is a block diagram of one embodiment of a DC microgrid buildingenergy management platform of the present invention.

FIG. 6 is a block diagram of one embodiment of a DCMG-BEMP including aphased installation plan of the present invention.

FIG. 7 is a block diagram of one embodiment of a DC building system ofthe present invention.

FIG. 8 is a block diagram of one embodiment of a DC power control systemof the present invention.

FIG. 9 is a block diagram of one embodiment of a DC load control systemof the present invention.

FIG. 10 is a block diagram of another embodiment of a DC power controlsystem of the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates embodiments of the invention, in several forms, theembodiments disclosed below are not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formsdisclosed.

DESCRIPTION OF THE PRESENT INVENTION

The present invention may: 1) showcase the viability and optimize theperformance of a building-level DC microgrid subsystem, 2) validate theefficiency improvements of DC-powered components relative toconventional AC components when powered by PV, 3) showcase the DCmicrogrid system's impact on energy security by providing backup powerfor mission-critical activities while minimizing the need for otherbackup energy sources, and 4) demonstrate the added value of energystorage in AC and DC load-leveling scenarios.

In one embodiment, the invention provides a core DC microgrid whichutilizes PV energy more effectively in common building loads. Anotherembodiment includes storage which may dramatically increase energysecurity. The DCMG-BEMP of the present invention addresses thelimitations of current building electrical power distribution systems byimplementing a separate DC electrical distribution microgrid and novelDC-based electrical loads. Directly utilizing DC power eliminates themultiple conversions (DC-AC and AC-DC) of typical AC systems. Mostrenewable energy production systems (solar, wind, etc.) are tethered tothe utility grid and allow for no direct usage of the power produced.The core DCMG-BEMP system architecture is designed to optimize theamount of renewable power used locally within the building. This coresystem also eliminates the expensive and unreliable grid-tie inverter.The DCMG-BEMP is further differentiated from other DC microgridapplications by an Energy Management Gateway (EMG), which manages theintegrated PV power production, DC loads, and DC sources to minimize theoverall (grid and renewable) energy use and total cost of ownership(TCO).

The system architecture simplifies building electrical wiring bysignificantly reducing wiring conduit runs, as many of the DC-basedcomponents are either roof- or ceiling-mounted (including the PV array,lighting, and ceiling-mounted ventilation fans), and can utilizeexisting AC wiring for DC power, making the system well suited toretrofit as well as new construction applications. The DCMG-BEMP issuitable to many facility types, since lighting and HVAC are largeenergy users in most buildings. As such, the DC loads may be commercialhigh-bay lighting and a large industrial ceiling fan that improves HVACsystem efficiency. This broad application base may allow market forcesto realize economies of scale and further improve thecost-effectiveness.

A DCMG-BEMP of the invention may include three phases, as shown in FIG.5, which is a high-level system schematic. A detailed block diagram isshown in FIG. 6. A core DCMG-BEMP system is first integrated in Phase I,which includes a PV array, DC power supply, and a DC-based high-bayinduction lighting system. This core system is relatively small and issized to match the DC loads, such that all PV production is immediatelyused. The result is a simple and cost-effective solution that does notrequire a grid-tied inverter. The core system may incorporateapproximately 20 kW of PV depending on the amount of building loads thatcan be converted to DC, but (unlike the latter Phases) the core does notsignificantly enhance the facility's energy security.

Phases II and III build on the core system by adding additional PVgeneration and energy storage to dramatically enhance the facility'senergy security and mission assurance during power outages. The managedenergy storage system also performs load leveling/peak load reductionunder normal operation to reduce utility costs. These phases requiresubstantially more PV power, and the functionality of the grid-tieinverter is integrated into the storage system to upload excess PV andstored power to the grid. A net metering agreement may allow for theuploaded energy to offset utility-supplied energy. Phase II integrates abattery-based energy storage system, large-diameter DC-powered ceilingventilation fans as an additional DC load, and added PV array capacity.Ceiling-mounted ventilation fans (e.g., 24 inch diameter) may be used asDC load, but a DC HVAC system, for example, may also be used. The fancirculates air so the heated/air-conditioned air is uniformlydistributed, and moving air provides more comfort to occupants. Theresult is that the HVAC system can be set to a lower or highertemperature (depending on the mode), and/or operates less often, usingless energy while maintaining occupant comfort. Each fan requires 1.5 kWto operate (3 kW total for two fans), which is substantially less thanthe HVAC power reduction. Use of large ventilation fans can reduce airconditioning energy consumption by 36%, reduce heating energyconsumption by 20+ %, and elevated air speed from a large fan canincrease productivity by 9% in non-air conditioned spaces.

Phase II integrates a battery energy storage system such as a GreenCharge Networks (GCN) GreenStation battery storage system to provideemergency backup power to critical DC loads. The GreenStation storagesystem may also demonstrate AC load-leveling features by actively usingthe system's energy storage capacity to level the building's demand forutility grid power when the system is not in emergency backup mode.Phase III integrates an additional PV generation and increased batterycapacity as well as an electric vehicle charging stations (EVCS). TheDCMG-BEMP-connected EVCS further supports mission-critical activities byproviding the ability to charge vehicles even during power outages, suchthat personnel mobility can be maintained throughout.

The Energy Management Gateway (EMG) performs overall system managementand interfaces with existing building network infrastructure (e.g.,LonWorks) if needed. The EMG provides maximum power point tracking(MPPT) algorithms that keeps the PV System operating at the highestpossible efficiency regardless of weather and load conditions. The EMG,together with the GCN GreenStation battery energy storage, also managesthe solar-synchronized loads (SSL) function, including AC and DCload-balancing and load-shedding to reduce non-critical loads duringperiods of reduced PV power (without affecting critical lighting orother loads). The EMG control software may be optimized and implementedto manage the DC power sources, lighting and fan systems, GreenStationenergy storage, and EVCS via secure, wired connections.

Supplemental grid power is supplied to the DC microgrid via an AC-to-DCpower supply when PV power alone is insufficient, and when stored poweris being conserved. Power flow is controlled by the EMG to optimize useof grid vs. solar vs. stored power. The EMG-controlled power suppliesrespond instantaneously to attenuate “peak-to-valley” changes duringrapidly varying solar energy production, such as during cloud-shadingevents. The EMG also determines and manages times at which it is mosteffective to charge the battery system from the PV array and/or utilitygrid, as well as times at which it is most effective to export PV and/orstored power to the building's other AC loads. The result minimizesgrid-based energy and power demands and maximizes renewable energyusage. The GreenStation's battery energy storage system'senergy-buffering capability also enables the Phase III EVCS installationto be done without “last-mile” grid upgrades, thus reducing costs.

The invention may provide a modular, scaleable, and optimized DCMG-BEMPsystem flexibly designed for broad commercial applications. An efficientDC infrastructure and EMG-managed device connectivity is an importantDCMG-BEMP feature, as it enables simplified DC microgrid “islanding” foroff-grid operation. Islanding of the DC microgrid allows critical loadsto be unaffected during blackouts by using PV and/or stored energy.High-priority loads such as lighting are reduced according to thefacility's emergency-mode requirements while lower-priority loads areallocated energy as it becomes available. As a result, the reliance onother backup power sources is eliminated or significantly reduced. Thisislanding capability is unique to the inventive system and an ideal fitfor providing backup power at mission-critical facilities and emergencyshelters. Conventional grid-tied inverter-based PV systems cannotprovide this backup functionality, as these systems turn off when gridpower is lost. A programmable emergency power mode may be integratedinto the EMG to manage tradeoffs between building lighting andventilation levels, battery storage capacity, and weather effects.

In one embodiment, the induction lights (Everlast), PV panels (Bosch),GreenStation (GCN), and DC power supply (Emerson) are all UL-certifiedcommercial units in serial mass-production. The equivalent DC version ofthe Everlast induction light (e.g. ballast, light, enclosure) may alsobe UL certified. The EMG may either be an off-the-shelf solution (e.g.Tridium) or may utilize mature software platforms (Visual Rules andInubit) operating on UL-certified hardware. The large commercial ceilingfans (Delta T Corp) are mass-produced. The fans are AC-powered, bututilize variable frequency drives (VFD) that operate internally on DCpower. Either the DC circuits of the existing VFD may be utilized, orthe VFD may be replaced/supplemented with a commercially availableDC-input device. In any case, the complete DC fan unit may be ULcertified and added in Phase II. A commercially available EVfast-charging station (e.g. Eaton DC Quick Charger) may be installed inPhase III. The charger may have an AC interface with the GreenStation.Integrating the EV fast charging station with a DC connection to theGreenStation may maximize the microgrid's benefits and capabilities.

-   Phase I: Install core DC microgrid including PV and DC lighting.    Compare performance vs. conventional AC system to validate economic    advantages.-   Phase II: Expand core system functionality to include large DC    ceiling fan. Add first elements of enhanced system to demonstrate    value of storage in improving energy security. Demonstrate emergency    backup and load-leveling with limited Phase II PV and storage    capacity.-   Phase III: Increase capacity of enhanced system by adding more PV    and storage, and install EV charging station. Demonstrate full value    of load-leveling and energy security features including EV charging    during blackout conditions.

The present invention may:

-   -   Demonstrate the total cost-of-ownership savings the system        provides as a result of improved energy efficiency, lower        upfront cost, lower operating and maintenance (O&M) costs, and        demand charge reductions. The invention may validate the        enhanced facility energy security from the DCMG-BEMP relative to        a conventional AC infrastructure. A small, conventional 10 kW PV        reference system with AC inverter and AC induction lighting may        be constructed next to the DC PV array as a comparison to the        core DC microgrid. Energy use and power demand of the        DC-microgrid and AC-reference systems may be directly compared        to quantify savings, as well as compared to the current system        (using historical data) to quantify the impact of the lighting        upgrade. HVAC energy usage for the baseline system and that        integrating the DC ventilation fans may be analyzed to quantify        the energy-consumption impact. O&M costs for the demonstration        system may be compared with the current infrastructure to        quantify the operating-cost and reliability impacts. Initial        economic analysis indicate the core DC microgrid        power-management functionality may have a net present value that        is less and a Savings to Investment Ratio (SIR) that is higher        than a comparable AC system.    -   Demonstrate the impact of effective optimized use and management        of renewable solar power to reduce grid-supplied energy and        power demands. Initial estimates based on simulation results of        the proposed core system indicate 8% to 12% less PV        infrastructure (panels, racking, wiring, etc.) in terms of        kilowatts are needed to provide the same PV energy to the        DC-based lighting as compared to the AC reference system. This        assumes the minimum Phase I system on the demonstration        facility, in which a small, 10 kW PV or 20 kW PV system is used        in a highly cost-effective way to supplement the lighting needs.    -   Demonstrate the DCMG-BEMP system's unique energy-security        enhancement by providing backup power for mission-critical        activities without requiring outside energy sources (e.g.        liquid/gaseous fuels). Tradeoffs between the PV array size and        battery storage versus energy security may be demonstrated in        terms of the probability of having sufficient power to keep the        facility functional throughout the day and night under various        weather conditions.    -   Two DC-based microgrid system architectures with broad        application may be demonstrated. The first “core” DC microgrid        system may utilize a relatively small PV array that may use PV        energy far more cost-effectively than conventional AC systems        when paired with DC loads, such as lighting and ventilation        fans. This system has broad application and is especially suited        to buildings operating seven days a week. The second “enhanced”        system is intended for buildings where energy security is of        primary importance. An optional energy storage system and        additional PV array are used to add a scalable amount of energy        security, reducing or completely eliminating the need for        on-site fuel storage for diesel generators. In addition to the        backup power functionality, the battery storage system's ability        to provide utility demand charge reduction and load leveling        (while also reducing the need for infrastructure upgrades) may        be demonstrated.    -   Additional Benefits: The increased renewable energy usage may        improve air quality and energy use.

The DCMG-BEMP may effectively reduce overall total cost of ownership fora building, maximize the use of renewable PV energy production tominimize grid-supplied energy, improve the energy-security andbackup-power capabilities relative to conventional AC infrastructure,and demonstrate the added value of energy storage for building loadleveling and peak load reduction.

TABLE 1 Quantitative Performance Objectives Summary PerformanceObjective Metric Data Requirements Renewable Energy Renewable EnergyUsed Meter readings of renewable Usage on Installation (kWh and energyused by installation; MMBtu) measured values from data acquisitionsystem Facility Utility Energy Energy Usage (kWh and Historical utilitystatements Usage (Electric, MMBtu) (current system); data acquisitionNatural Gas, etc.) system measurements of facility energy usage PeakElectric Utility Monthly Peak Power Historical utility statements LoadReduction (kW) (current system); data acquisition system measurements offacility peak power Annual Operating Lighting and HVAC data acquisitionsystem Costs (includes energy Energy Costs ($/year), measurements ofcurrent facility usage and maintenance Maintenance Costs lightingenergy; lighting costs) ($/year) maintenance records (parts and laborcosts) Facility Energy Time without Utility Time-stamped dataacquisition Security/Backup Grid Power during Grid system measurementsof facility Power Availability Interruptions (hours) energy use duringpower outages Ensure Lighting Candle Power of Light at Handheld lightintensity meter Output Fulfills Best Ground Level (target is PracticeStandards 50 foot candles) System Scalability and Number of ApplicableDetailed facility inventory data Transferability Facilities in Current(square footage, building type and Inventory use, ceiling height, annualelectric usage, etc.) System Economics Internal Rate of Return Utilitystatements; installation and (IRR) (%), Annual Cost operational costs;discount rates; Savings ($), Payback usable lifetimes; etc. Period(years)

-   -   Phase I—Core DCMG-BEMP system with an approximately 20 kW PV        array to power DC-based lighting. The size of the system may be        based on the amount of lighting loads that can be converted        to DC. A small (10 kW) AC-based reference system may be used to        collect baseline data for direct comparison.    -   Phase II—The Phase I system plus an additional 35 kW PV, a 32        kWh battery storage system, and a DC-powered large-diameter        ceiling fan.    -   Phase III—The Phase II system plus an additional 35 kW PV (for        100 kW total) PV, an additional 64 kWh of battery storage (for        96 kWh total), and a fast-charge electric vehicle charging        station.

a) Phase I

Phase I may include the following:

-   I-1.Baseline the energy usage and lighting level of the current AC    lighting for comparison to the Phase I system. Begin long-term data    acquisition of the HVAC system and a complete building electrical    energy profile to use as a baseline in the Phase II load-leveling    demonstration.-   I-2.Demonstrate how the core DC microgrid system operates without a    grid-tied PV inverter and more efficiently transfers energy to DC    lighting loads (relative to the conventional reference PV system    utilizing an inverter and AC-based lights).-   I-3.Update the economic analysis comparing the DC microgrid relative    to an equivalent AC system by incorporating the measured efficiency    improvements, installation differences, and projections of    reliability/maintenance differences.-   I-4. Collect summer and winter HVAC temperature settings prior to    installation of DC fan in Phase II.

(1) Task PI-1—Demonstration Site Selection

The ideal DCMG-BEMP system site is a large, high-ceiling building (suchas a warehouse, gymnasium, commissary, vehicle maintenance garage,aircraft hangar, etc.) that can accommodate a PV array and high-baylighting. The ideal facility would also be used as an emergency shelter.The ideal building has a large roof, seven-days-a-week operation, and anelectrical consumption pattern generally aligned with the PV system'senergy production. Daily operation is critical because PV array in thecore system is sized to directly power the lights, eliminating the needfor a grid-tie inverter to feed power back into the grid. The DCMG-BEMPand EMG are flexible, scalable technologies that optimize energy use inall climate zones and building sizes, from small structures up to entireclusters of buildings.

(2) Task P1-2—Quantify Baseline System Performance

Energy Usage/Power Demand—A data acquisition system may be installed tocollect electricity usage data for system components as well as thewhole facility to characterize the baseline utilization profile. Thesedata sets may be analyzed to determine the baseline system performance,including daily, monthly, average monthly, and annual energy usage (kWhand MMBtu), electricity demand (kW), and demand charges ($), as well asthe frequency of utility grid failure events (i.e. blackouts). Thisinformation may also be used to optimize the EMG control software forthe demonstration site's operating characteristics.

Operating and Maintenance Costs—Historical maintenance and replacementcosts (including parts and labor) may be collected and analyzed todetermine typical, annualized equipment-maintenance costs. Thisinformation may be used within the DCMG-BEMP system's cost-effectivenessand payback calculations.

Light Output Test—An evaluation of floor-level lighting may be doneusing a handheld light intensity meter. Data points may be taken along avirtual grid across the gymnasium floor to capture any potentialvariations. The test may be performed once to quantify the inductionlighting's output goal (Task PI-3).

a. Task PI-3—Phase I System Integration Design and Installation

To allow for a direct comparison, the Phase I system may be segmentedinto two subsystem circuits: (1) the core DC system (min. 20 lightfixtures), and (2) a smaller reference AC system (4 light fixtures) thatmay serve as a control to determine the DC system's reduction inlighting power consumption. This AC system may allow for energy usagecomparisons in validating the DCMG-BEMP system's performance. Thisreference system requires the addition of a PV inverter to provideenergy to the AC-powered lights.

The Phase I system includes installation of: (1) a 30 kW rooftop solarPV array, (2) an Emerson NetSure 4015 System 30 kW, 400 V AC-DC powersupply, (3) a Bosch Energy Management Gateway, (4) a Solectria 10 kW PVinverter, (5) min 24 Everlast EHBUS-RC 250 W induction lights (20DC-powered and 4 AC-powered), and (6) the required electrical wiring. Alighting study was completed to determine the number and power rating ofthe induction lights. The current 400 W metal-halide light fixtures maybe replaced, with wiring reused wherever possible. Understanding howexisting AC wiring can be reused for DC circuits is very important forfuture retrofit applications. The design may meet current electricalcodes and standards, as well as Fort Bragg's design guidelines. All ofthe components used may be UL certified.

Certain aspects of the hardware design (such as available space, wiring,etc.) may be designed anticipating Phase II and III tasks. FIG. 6provides a system schematic, including the phased installation plan forthe major hardware elements. This phased installation approach ensuresthat sufficient capacity is available for each phase, while evening outmonetary expenditures.

b. Task PI-4—Phase I DCMG-BEMP Operation, Data Collection, and Analysis

System Performance Analysis—Once installed and commissioned, theDCMG-BEMP system may be operated to collect electricity usage data. Datacollection may continue to ensure that seasonal changes are accuratelycaptured. The EMG may serve as a data acquisition system, recording theenergy and power usage throughout the demonstration. Since electricaldemand charges are typically defined as the highest average 15-minutepeak power in a given billing cycle, the data acquisition algorithm maybe flexible to capture regular interval data (e.g. 1-second or 5-seconddata). The same data parameters used for baseline system analysis may becollected in this task, including energy usage (kWh and MMBtu) anddemand (kW) data. This data and non-electricity utility statements (e.g.natural gas) may be analyzed to determine the DCMG-BEMP system'sperformance, including daily, monthly, average monthly, and annualenergy usage (kWh_(Total), kWh_(Grid-Supplied), and MMBtu), renewableenergy usage (kWh), electricity demand (kW_(Total) andkW_(Grid-Supplied)), and demand charges ($).

2. Phase II

Phase II may include the following:

Add a DC fan as an additional load within the DC microgrid. The fan canreduce the heating and cooling loads of the current HVAC system, thussaving energy.

Additional energy security may be offered by adding a GCN GreenStationwith 32 kWh of battery storage, as well as 35 kW of PV. Specifically,the amount of backup time available during a blackout at differentemergency lighting levels and various weather conditions may beincreased.

The load-leveling capabilities may be offered by linking theGreenStation to the building AC circuits, offering the ability tocompensate for wide, rapid variations in PV power generation andbuilding loads (from HVAC, etc.) by discharging and charging the batterystorage appropriately.

The DC fan's speed can be varied to match the amount of PV poweravailable (on a daily, seasonal, and/or weather-influenced basis) tofurther level the building load profile.

a. Task PII-1—Phase II System Integration Design and Installation

The Phase II system builds on the Phase I system by adding: (1) 35 kW ofrooftop solar PV array capacity (65 kW total), (2) a 32 kWh GCN batterystorage system, (3) two 24 inch-diameter ventilation fans, and (4) EMGmodifications. The draft SOW includes the installation upgrade plans forthese components. The same installation subcontractors used in Phase Imay be used in both Phase II and Phase III.

b. Task PII-2—Phase II DCMG-BEMP Operation, Data Collection, andAnalysis

3. Phase III

Phase III may include the following:

Additional energy security may be offered by increasing the GCNGreenStation capacity to a total of 96 kWh of battery storage and 70 kWof PV. Specifically, the amount of backup time available during ablackout at different emergency lighting levels, demonstrated undervarious weather conditions may be increased.

Additional load-leveling capabilities may be due to the increasedGreenStation capacity.

The addition of a fast-charge EVCS to the GreenStation can effectivelybe used as part of the load-leveling strategy.

The EVCS can continue to be used during an emergency blackout scenarioby utilizing PV and stored energy, further increasing the energysecurity of the demonstration site.

A battery storage system and EVCS with DC connectivity offers the samefunctionality as the current AC-powered scenario, while offeringimproved efficiency during backup and charging operations.

a. Task PIII-1—Phase III System Integration Design and Installation

The Phase III system builds on Phase II's system by adding: (1) 35 kW ofrooftop solar PV array capacity (100 kW total), (2) an additional 64 kWhof GCN battery storage (96 kWh total), (3) a fast-charge EVCS, and (4)EMG modifications. The draft SOW includes the installation upgrade plansfor these components.

a. Task PIII-2—Phase III DCMG-BEMP Operation, Data Collection, andAnalysis

System Performance Analysis—The same data parameters used in baselinesystem analysis, Phase I, and Phase II may be collected in this task,including energy usage and demand data. This data and non-electricityutility statements may be analyzed as detailed above (in the SystemPerformance Analysis of Task PI-4) to determine the DCMG-BEMP system'sperformance under Phase III operation.

-   -   a. Load-Leveling/Peak Power Reduction—Two system        configurations: (1) with a fully functional GreenStation        utilizing the energy storage and the EMG's energy-management        algorithms managing the energy usage of all DC microgrid        components (lights, fans, energy storage, and EVCS), and (2)        with the energy storage disconnected from the building and the        EMG's energy-management algorithms managing the energy usage of        all remaining DC microgrid components (lights, fans, and EVCS).    -   b. Avoidance of Technical Risks

The control algorithms are developed such that, if a code failureoccurs, the system may fail in a way that allows DC devices to bepowered from the grid to ensure building loads are not interrupted.

The battery system is not in the critical path of electrical energytransfer (i.e., from the DC power supply and PV array to the lightingsystem), so building functions may continue to operate normally even asthe battery's capacity decreases throughout its lifetime. The energystorage system may be tested periodically without affecting buildingfunctionality; any faults or reductions in capacity may be reportedaccordingly.

The installation assumes that the existing AC wiring can be reused forthe majority of the DC microgrid wiring. If this is not possible,separate DC wiring runs may be needed (requiring additional installationhardware and labor, permitting/inspections, etc.).

The ability to island the facility from the utility grid during a poweroutage or an emergency is an inherent DCMG-BEMP feature, as it does notrequire a grid-tied PV inverter. Islanding allows the building's DCloads to continue functioning during such events, enhancing thefacility's energy security. Depending upon building application, theemergency power mode may reduce or eliminate the need for backupgenerators (and their associated fuel usage). The inventive system isscalable and ideally suited to large, flat-top buildings with high-baylighting.

The ceiling fan, especially the large commercial variety made bycompanies like Delta T, may be an appropriate DC load to complement DClighting (or standalone) in the inventive DC microgrid. The ceiling fanis a load that inherently synchronizes very well to the solar PVgeneration, and can also be varied in speed to match the desired loadconditions (for example, to help get the system to maximum power point(MPP) of the PV at any exact moment).

The DC fan's speed can be varied to match the amount of PV poweravailable (on a daily, seasonal, and/or weather-influenced basis) tofurther level the building load profile. Ceiling fans are especiallywell suited to PV power generation because they generally run at ahigher speed in summertime (to help cool building occupants, allowing ahigher air-conditioning thermostat setting, overall saving HVAC energycost), and run at a lower speed in wintertime (just to bring hot airfrom the ceiling down to the floor level where the occupants are,allowing the heating system to run less often, with less heat lossthrough the ceiling, overall saving HVAC energy). This can be done inthe same rotational direction winter/summer or reversing directions withseason (typically blowing air down in summer). If the profile of thesummertime/wintertime fan speed and resulting energy use is matched tothe solar PV generation, this can result in a more optimized size of thePV array for the DC microgrid, since the case where substantially allthe PV energy from the PV array is consumed locally through DC loads mayresult in the best economics for the DC microgrid and shortest paybackfor the PV elements. Synchronization of the fan load to other variationsin PV generation (daily variation from morning to night, variations dueto weather such as short-term cloud events, etc.) are also possible forboth DC microgrid configurations and conventional AC systems where an ACPV inverter is connected to an AC fan. This synchronization can also becoordinated with the other building loads, and especially in the DC casecan be part of a system-level PV power point tracking system which wouldkeep the PV operating at the optimum power point for the currentsituation. In any case (AC fan load or DC fan load), consuming locallygenerated PV energy locally in the building loads whenever possibleresults in lower economic and energy losses which may be associated withconsuming power from the utility grid that is generated remotely, andassociated with sending excess PV power out to the grid, only to have aneed for that same PV energy in the building loads at a later time.

FIG. 7 illustrates a DC building system 700 including a renewable energyDC power source in the form of a solar device 702 whose output isconnected to a DC bus 704. In bi-directional communication with DC bus704 is a source of DC power in the form of a DC power supply 706. DCpower supply 706 may include an energy storage device in the form of abattery 708, a DC/DC converter 710, an AC/DC inverter 712, and aprocessor in the form of a controller 714. As used herein, the term “DCpower supply” may encompass any device that provides DC electricalenergy converted from another form of energy, such as AC electricalenergy, or chemical energy in the case of a battery.

Both solar device 702 and DC power supply 706 may provide DC electricalpower to DC bus 704. An AC grid 716 may provide AC power to DC powersupply 706, which AC/DC inverter 712 may convert to DC power. DC powerconsuming devices or variable DC loads in the form of DC lights 718, DCthermal device 720, and DC fan 722 may draw DC power from DC bus 704. DCfan 722 may include a motor or generator that is capable of operating ina regenerative mode.

FIG. 8 illustrates a DC power control system 800 including a renewableenergy DC power source in the form of a solar device (e.g., aphotovoltaic array) 802 whose output is connected to a DC bus 804. Solardevice 802 and DC bus 804 are in communication with a source of DC powerin the form of a DC/DC converter 810 and an AC/DC inverter 812, and witha processor in the form of a controller 814. An energy storage device inthe form of battery 808 may provide DC power to DC bus 804.

Solar device 802, battery 808, and an AC power source in the form of anAC grid 816 may supply DC electrical power to DC bus 804. AC/DC inverter812 may convert AC power supplied by AC grid 816 to DC power. DC powerconsuming devices or variable DC loads in the form of DC lights 818, DCthermal device 820 (e.g., a freezer), and DC fan 822 may draw DC powerfrom DC bus 804. Accordingly, it will be appreciated that the DC powerconsuming devices or variable DC loads can receive power from one ormore of solar device 802, battery 808, and AC grid 816 via a commonpower distribution circuit (not shown). DC fan 822 may include a motoror generator that is capable of operating in a regenerative mode.Optionally, one or more energy storage elements 824 may be connectedindependently and/or directly to DC bus 804.

FIG. 9 illustrates a DC load control system 900 which may beincorporated into DC building system 700 and/or DC power control system800. Accordingly, DC load control system 900 will be described withreference to components of power control system 800. DC load controlsystem 900 includes a second controller 902 interconnecting DC bus 804and DC power consuming devices or variable DC loads in the form of DCbuilding lights 918, DC thermal device 920, and DC fan 922. Each ofthese variable DC loads may draw DC power from DC bus 804. DC buildinglights 918 may include emergency lights 924 and other lights (e.g.,non-emergency lights) 926. Emergency lights 924 may draw less power thanthe entirety of DC building lights 918 and may be a subset of DCbuilding lights 918. Emergency lights 924 and DC fan 922 may function asDC emergency loads which operate when neither solar device 802 nor theother sources of DC power 810, 812 are operable. For example, energystorage device 808 may power each of the DC power consuming devices 918,920, 922 in conjunction with solar device 802 and the other sources ofDC power 510, 512 under normal non-emergency operating conditions.However, under emergency operating conditions (e.g., when a storm hasdisabled the AC grid and the solar device), energy storage device 808may power the DC emergency loads 922, 924 for a predetermined period oftime when no source of power other than the energy storage device 808 isavailable to the DC power consuming devices 918, 920, 922. Secondcontroller 902 may respond to solar device 802 and the DC power supply810, 812 being inoperable for a threshold length of time by reducing alevel of power drawn by at least one of the DC power consuming devices918, 920, 922.

DC fan 922 may operate at a slower speed in an emergency mode than in anon-emergency mode. In another embodiment, emergency lights are the sameas non-emergency lights, but the lights draw less power and are dimmerin an emergency mode than in a non-emergency mode. In anotherembodiment, the emergency lights are a subset of the non-emergencylights.

Controller 714 and/or controller 814 may function as a DC power controlsystem which charges the energy storage device during time periods inwhich the source of DC power is operable, and which discharges theenergy storage device during time periods in which the source of DCpower is inoperable. The charging and discharging may be based on acurrent state of charge (SOC) of the energy storage device and apredetermined target SOC of the energy storage device. For example,charging of the energy storage device may take place only if and/orwhenever the current SOC or voltage level of the battery is below adesired target SOC or voltage level of the battery. Discharging of theenergy storage device may take place only if and/or whenever the currentSOC or voltage level of the battery is above a desired target SOC orvoltage level of the battery. The predetermined target SOC may be astate or level of charge or voltage that is sufficient to solely powerat least one of the DC power consuming devices for a predeterminedduration of time while the source of DC power is inoperable (e.g.,during a lightning storm).

The DC power control system 800 may charge the energy storage device 808by using excess power from the renewable energy DC power source 802. TheDC power control system 814 may respond to the current SOC of the energystorage device dropping below the predetermined target SOC by adjustingat least one of the variable DC power consuming devices 818, 820, 822such that a level of current drawn by the variable DC power consumingdevice 818, 820, 822 is less than a level of current sourced by therenewable energy DC power source 802, and such that the energy storagedevice 808 is charged to the predetermined target SOC by the renewableenergy DC power source 802.

The DC power control system 800 may respond to the current SOC of theenergy storage device 808 dropping below the predetermined target SOC byadjusting a discharge current rate of the energy storage device 802 byselectively reducing or discontinuing operation of at least one of thevariable DC power consuming devices 818, 820, 822 dependent upon abuilding ambient condition and/or a corresponding predetermined buildingcondition. In one embodiment, the building ambient condition includes alevel of sunlight. In one embodiment, the corresponding predeterminedbuilding condition includes a desired emergency interior lighting level.In related embodiments, DC power control system 800 selectively reducesoperation or discontinues one or more of DC lights 818 such that a levelof light provided by DC lights 818 supplements the level of sunlight tomeet the desired emergency interior lighting level. In this way, DCpower control system 800 can control a discharge rate of battery 808and, more particularly, can reduce the discharge rate by lowering anumber of the DC lights 818 operating to meet the desired emergencyinterior lighting level.

The DC power control system 800 may respond to the source of DC power810, 812 being inoperable for a threshold period of time by adjusting atleast one of the variable DC power consuming devices 818, 820, 822 suchthat a level of current drawn by the variable DC power consuming device818, 820, 822 is thereby reduced. Moreover, the DC power control system800 may selectively reduce or discontinue operation of at least one ofthe variable DC power consuming devices 818, 820, 822 dependent upon alength of time during which the source of DC power 810, 812 has beeninoperable.

The DC power control system 800 may charge the energy storage device 808by discontinuing power to the motor or generator of the DC fan 822 andby operating the motor or generator in a regenerative mode in whichkinetic energy of the motor or generator is converted to DC power.

The DC power control system 800 may control amounts of DC power providedto the DC bus 804 by the solar device 802 and by a DC power supply 810,812 that is fed by the AC grid 816. Particularly, the DC power controlsystem 814 may control how much power is provided by the solar device802 and how much power is provided by the DC power supply 810, 812dependent upon how much power is needed by the DC power consumingdevices 818, 820, 822, the cost of the AC power from the grid 816, howmuch power is available from other sources, such as an energy storagedevice 808, a motor operating in a regenerative mode, etc.

FIG. 10 illustrates another embodiment of a DC power control system 1000which may be substantially similar to DC power control system 800,except that system 1000 additionally includes a mobile device in theform of a motorized vehicle 1028 powered by battery 1008. DC powercontrol system 1000 includes a renewable energy DC power source in theform of a solar device (e.g., a photovoltaic array) 1002 whose output isconnected to a DC bus 1004. Solar device 1002 and DC bus 1004 are incommunication with a source of DC power in the form of a DC/DC converter1010 and an AC/DC inverter 1012, and with a processor in the form of acontroller 1014. An energy storage device in the form of battery 1008may provide DC power to DC bus 1004.

Both solar device 1002 and the DC power supply may provide DC electricalpower to DC bus 1004. An AC grid 1016 may provide AC power to the DCpower supply, which AC/DC inverter 1012 may convert to DC power. DCpower consuming devices or variable DC loads in the form of DC lights1018, DC thermal device 1020 (e.g., a freezer), and DC fan 1022 may drawDC power from DC bus 1004. DC fan 1022 may include a motor or generatorthat is capable of operating in a regenerative mode. Optionally, one ormore energy storage elements (not shown) may be connected independentlyand/or directly to DC bus 804.

Motorized vehicle 1028 may be in the form of a golf cart or a fork lift,for example. Thus, the energy storage device may power the DC powerconsuming devices in conjunction with the solar device and the othersource of DC power, and may also power the motorized vehicle.Accordingly, battery 1008 may substantially simultaneously perform bothfunctions of providing emergency power for emergency loads when thesolar device and the other source of DC power are inoperable, and beingthe exclusive source of power for a motorized vehicle.

It is to be understood that the present invention may encompassembodiments in which ceiling fans or other motor loads act in aregenerative braking mode as all or part of the energy storage to powerthe lights directly. That is, the regeneration may not necessarilycharge other batteries in the system. In other words, if there are nobatteries in the system, the fans slowing down could keep supplyingpower to the DC lights when the grid is lost. This method may helpfill-in power when a cloud passes and suddenly solar power is lost. Thismay increase the life of the DC power supply because the DC power supplydoes not have as large of a power surge due to sudden clouds if the fanmotors help supply even a small amount of energy storage.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

What is claimed is:
 1. A DC building electrical system comprising: a DCbus; a DC power consuming device connected to the DC bus; a source of DCpower connected to the DC bus and configured to power the DC powerconsuming device; a DC emergency load; and an energy storage deviceconnected to the DC bus and to the DC emergency load, the energy storagedevice being configured to: power the DC power consuming device inconjunction with the source of DC power; and power the DC emergency loadwhen no source of power other than the energy storage device isavailable to the DC power consuming device.
 2. The system of claim 1,wherein the source of DC power comprises: a photovoltaic array producinga DC voltage on the DC bus; and/or a DC power supply producing DCvoltage on the DC bus from AC voltage received from a utility grid. 3.The system of claim 1, wherein the energy storage device is configuredto power the DC emergency load for a predetermined period of time whenno source of power other than the energy storage device is available tothe DC power consuming device.
 4. The system of claim 3, furthercomprising a renewable energy DC power source connected to the DC busand configured provide power to the DC emergency load in conjunctionwith the energy storage device when no source of power other than theenergy storage device is available to the DC power consuming device. 5.The system of claim 1, wherein the DC emergency load is included in theDC power consuming device and is configured to draw less power than theDC power consuming device.
 6. A DC building electrical systemcomprising: a DC bus; a DC power consuming device connected to the DCbus; a source of DC power connected to the DC bus and configured topower the DC power consuming device; a motorized vehicle; and an energystorage device connected to the DC bus and to the motorized vehicle, theenergy storage device being configured to: power the DC power consumingdevice in conjunction with the source of DC power; and power themotorized vehicle.
 7. The system of claim 6, wherein the energy storagedevice is configured to be an only source of power for the motorizedvehicle.
 8. The system of claim 6, wherein the motorized vehiclecomprises a golf cart or a fork lift.
 9. A DC building electrical systemcomprising: a DC bus; a DC power consuming device connected to the DCbus; a source of DC power connected to the DC bus and configured topower the DC power consuming device; an energy storage device connectedto the DC bus and configured to power the DC power consuming device inconjunction with the source of DC power; and a DC power control systemconfigured to selectively charge and discharge the energy storage devicebased on a current state of charge of the energy storage device and apredetermined target state of charge of the energy storage device. 10.The system of claim 9, wherein the DC power control system is configuredto charge the energy storage device during time periods in which thesource of DC power is operable and discharge the energy storage deviceduring time periods in which the source of DC power is inoperable, thepredetermined target state of charge being a state of charge that issufficient to solely power the DC power consuming device for apredetermined duration of time while the source of DC power isinoperable.
 11. The system of claim 9, further comprising a renewableenergy DC power source connected to the DC bus, wherein the DC powercontrol system is configured to charge the energy storage device byusing excess power from the renewable energy DC power source.
 12. Thesystem of claim 9, further comprising a renewable energy DC power sourceconnected to the DC bus, wherein the DC power consuming device isvariable, the DC power control system being configured to respond to thecurrent state of charge of the energy storage device dropping below thepredetermined target state of charge by adjusting the variable DC powerconsuming device such that a level of current drawn by the variable DCpower consuming device is less than a level of current sourced by therenewable energy DC power source, and such that the energy storagedevice is charged to the predetermined target state of charge by therenewable energy DC power source.
 13. The system of claim 9, furthercomprising a renewable energy DC power source connected to the DC bus,wherein the DC power consuming device is variable, the DC power controlsystem being configured to respond to the current state of charge of theenergy storage device dropping below the predetermined target state ofcharge by adjusting a discharge current rate of the energy storagedevice by selectively reducing or discontinuing operation of thevariable DC power consuming device dependent upon a building ambientcondition and a corresponding predetermined building condition.
 14. Thesystem of claim 13, wherein the building ambient condition comprises alevel of sunlight.
 15. The system of claim 13, wherein the correspondingpredetermined building condition comprises a desired emergency interiorlighting level.
 16. The system of claim 9, further comprising arenewable energy DC power source connected to the DC bus, wherein the DCpower consuming device is variable, the DC power control system beingconfigured to respond to the source of DC power being inoperable for athreshold period of time by adjusting the variable DC power consumingdevice such that a level of current drawn by the variable DC powerconsuming device is thereby reduced.
 17. The system of claim 9, whereinthe DC power consuming device is variable, and wherein the DC powercontrol system is configured to selectively reduce or discontinueoperation of the variable DC power consuming device dependent upon alength of time during which the source of DC power has been inoperable.18. The system of claim 9, wherein the DC power consuming devicecomprises a motor or a generator, the DC power control system beingconfigured to charge the energy storage device by discontinuing power tothe motor or generator and operating the motor or generator in aregenerative mode in which kinetic energy of the motor or generator isconverted to DC power.
 19. A microgrid system arrangement comprising: aphotovoltaic array producing a DC voltage on a DC bus; a DC power supplyproducing DC voltage on the DC bus from AC voltage received from autility grid; a DC power consuming device connected to the DC bus; and acontroller configured to control amounts of DC power provided to the DCbus by the photovoltaic array and by the DC power supply.
 20. Thearrangement of claim 19, further comprising an energy storage deviceconnected to the DC bus, the controller being configured to cause theenergy storage device to: power the DC power consuming device inconjunction with the photovoltaic array and/or the source of DC power;and be an exclusive provider of power to the DC power consuming devicewhen the photovoltaic array and the DC power supply are inoperable. 21.The arrangement of claim 20, wherein the controller is configured toselectively charge and discharge the energy storage device based on acurrent state of charge of the energy storage device and a predeterminedtarget state of charge of the energy storage device, the predeterminedtarget state of charge being a state of charge that is sufficient tosolely power the DC power consuming device for a predetermined durationof time while the photovoltaic array and the DC power supply areinoperable.
 22. The arrangement of claim 19, wherein the controllercomprises a first controller, the arrangement comprising a secondcontroller configured to respond to the photovoltaic array and the DCpower supply being inoperable for a threshold length of time by reducinga level of power drawn by the DC power consuming device.